The Mycobacterium avium complex (MAC) consists of multiple Mycobacterium avium subspecies that can be found as environmental contaminants in soil and water and as infectious agents infecting animals such as pigs, cattle, sheep and birds. Organisms classified in the MAC complex include Mycobacterium avium subsp. avium (MAA), Mycobacterium avium subsp. paratuberculosis (MAP), Mycobacterium avium subsp. silvaticum (MAS), and Mycobacterium subsp. hominissuis (MAH). Symptoms of infection vary by host species and MAC organism. Of these MAC organisms, MAP is a bacterium that causes Johne's disease (chronic granulomatous enteritis of the small intestine) in livestock. Johne's disease results in decreased milk production, fetal loss, diarrhea and early death resulting in substantial economic loss to the livestock and diary industry.
The Mycobacterium avium subspecies classifications are complicated and inconsistent throughout the literature. Absent a systematic whole-genome sequencing effort for sequencing all Mycobacterium avium organisms, some Mycobacterium avium organisms are placed into subspecies based on what species they infect rather than on nucleic acid sequence similarity. Furthermore, mixed infections have also been described in the literature, further complicating classification and diagnosis.
Assays for the rapid, sensitive and specific detection of infectious pathogens are needed for differential identification of MAP and other Mycobacterium avium subspecies, which include MAA, MAH and MAS. Such assays are sought for differential and specific diagnostic identification of which microbe is infecting an animal.